Cortana
But Microsoft's Cortana assistant is available on Android and Apple's iOS, so the company has a way onto plenty of devices other than PCs.
that depends... Cortana is not available in the Apple Store on my iPad, though it is available on my iPhone. And I had to go looking for it. And Siri ships with both my iPad and iPhone, and I turn it off first thing, so I'm not actually going to install and run something from MS. Most people will just use what's on their devices in the first place, or, more likely, will just ignore Siri or whatever and never even think of installing Cortana.